Saturable magnetic core control device



April 6, 1954 F. P. SCHWIEG, JR 2,674,705

SATURABLE MAGNETIC CORE CONTROL DEVICE k Filed July 9, 1952 lnv enter: Frederic F. Schvui e59).

His Attorney.

Patented Apr. 6, 1954 UNITED STATES ATENT OFFICE SATURABLE MAGNETIC CORE CONTROL DEVICE New York Application July .9, 1952, serial N6. 291.818

My invention relates to improvements in saturable magnetic core control devices of the type wherein a magnetic flux, termed the control flux, controls the amplitude and phase of an electric signal, which may in turn control a servomotor for adjusting to a null position a permanent magnet which provides a portion of the control flux.

In particular, my invention relates to improvements in that type of control device which com prises a magnetic core having two saturable parts through both of which simultaneously pass two magnetic fiuxes, which may be called the excitation flux and the control flux respectively. These two fluxes simultaneously aid each other in one of the saturable parts, and oppose each other in the other saturable part, thus saturating these parts unequally to a degree which depends upon the magnitude of the control flux. In consequence of the unequal saturations, voltage is induced in a signal winding which is balanced with respect to equal fluxes in the two saturable parts.

In control devices of this type heretofore known, the excitation flux may be produced by passing alternating current through an excitation winding, and magnetic saturation occurs twice during each cycle of this excitation current. As a result, the induced voltage in the signal winding is largely at the second harmonic frequency of the excitation current. However, it is often desirable, for the control of servomotors or the like, to have the electric signal at the fundamental frequency of the excitation current. While magnetic control devices which produce a fundamental-frequency signal are well known, such as those which employ a bridge-type circuit, they are generally less stable with respect to zero drift, are more expensive to manufacture, or have other disadvantages.

' A principal object of my invention is to provide an improved saturable magnetic core control device which supplies, to a servomotor for example, an electric signal at the fundamental frequency of the excitation current, yet has the simplicity, stability and economy of manufacture usually associated with devices of the second harmonic type. Other objects and advantages will appear as the description proceeds.

Briefly stated, in accordance with one aspect of my invention, I connect a half-wave rectifier in series with the excitation winding of my device, and thus pass pulsating direct current through the excitation winding. This produces a pulsating excitation flux which, in conjunction with the control flux, produces magnetic saturation in the core but once each cycle of the excitation current,

and induces voltage in the signal winding which is largely at the fundamental frequency of the excitation current.

My invention will be better understood from the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the drawing, the single figure is a diagrammatic illustration of a preferred embodiment of my invention.

Referring to the drawing, a magnetic core memher I has two saturable outer legs 2 and 3, and also has a center leg 4 having a gap therein as shown. an excitation winding consists of two series-connected balanced halves 5 and 6 wound upon legs 2 and 3 respectively. Alternating current connections 1 and a half-wave rectifier 8 are in series with the excitation winding, as shown, and provide therethrough a pulsating direct current which produces a pulsating magnetic flux, termed the excitation flux, in core member I. The respective polarities of the excitation winding halves are such that the excitation flux flows downward through leg 2 and upward through leg 3 of the core.

A signal winding consists of two series-connected balanced halves 9 and ill wound upon legs 2 and 3 respectively. Electrical connections ll, including a series reactor 12, are provided whereby an electric current of variable magnitude and direction, termed the control current, may be applied to the signal winding. In flowing through the signal winding, the control current produces a portion of a magnetic flux termed the control flux. Another portion of the control flux is produced in a manner hereinafter explained. The polarities of signal winding halves 9 and H) are such that the magnetic flux produced by the control current flows in the same direction through legs 2 and 3, either upward or downward depending upon the direction of the control current.

A cylindrical, permanent magnet I3, magnetized transversely along a diametrical plane, as indicated by the reference letters N and S in the drawing, is located in the gap of center leg 4, as shown. Magnet l3 provides the other portion of the control flux. The angular position of the permanent magnet is adjustable as hereinafter xplained. Assume that magnet I3 is adjusted so that its plane of magnetization is vertical. Flux from the magnet passes upward through center leg 4, and downward through outer legs 2 and 3, or the reverse, depending upon the position of the magnet. Now, assume that magnet 13 is adjusted 3 to have its plane of magnetization horizontal. No net flux from the magnet passes vertically through legs 2 and 3. Intermediate positions of magnet 13 provide intermediate values of flux through legs 2 and 3.

The total control flux is the algebraic sum of the portions provided by magnet l3 and the control current respectively. In operation, the position of the magnet is adjusted automatically to a null position, as hereinafter explained, at which that portion of the control flux provided by mag net I3 is equal and opposite to that portion of the control flux provided by the control current flowing through the signal winding- When so adjusted, each position of the permanent magnet corresponds to a unique value in magnitude and direction of the control current.

From the foregoing description, it will be appreciated that the excitation flux and the control flux are simultaneously in mutually aiding relas tion in one of the saturable legs, and in mutually subtractive relation in the other saturable leg. It will also be appreciated that the signal winding' is in balanced relation to equal amounts of the pulsating excitation flux in the two saturable legs, so that, in the absence of control flux, the excitation flux induces equal but opposite alternating voltages in the two balanced halves 9 and III of the signal Windingand no net induced voltage occurs across the whole of the signal 1 winding.

Magnetic saturation occurs in one or both of the saturable legs 2 and 3 at the peak values, once each cycle, of the pulsating excitation flux. In the absence of a net control flux, both saturable legs become equally saturated, so that equal amounts of pulsating-flux pass through both legs, and no net induced voltage appears across the signal winding. However, in the presence of a control flux which aids the excitation flux in one saturable leg, while opposing itvin the other, the two legs become unequally saturated, and in consequence, unequal amounts of pulsatingfiux pass through the two legs. This induces a larger voltage in one half of the signal winding than in the other half, and the difference between these induced voltages appears as an electric signal across the'whole of the signal winding. Since saturation occurs but once during each excitation cycle, this signal voltage is largely at the same frequency, and is either 90 or 270 out of phase with the fundamentalfrequency alternating component of the pulsating excitation current.

The phase relation between the induced signal and the excitation current depends upon whether leg 2 or leg 3 is the more highly saturated, and hence depends upon the direction of the control flux; Thus, each reversal in direction of the control flux is accompanied by a phase reversal of the alternating electric'signal across the signal winding.

Magnet I3 is mechanically connected to a servomotor II, by a shaft for example. Operation of the servomotor adjusts the angular position' in the magnet, and thus adjusts the magnitude anddirection of a portion of the control flux. servomotor I4 is of a well-known type having afield winding connected to terminals Wand a control winding connected to terminals l1, and having a rotor connected to shaft 15 which is capable of rotation in either direction selectively, depending upon the phase relation of alternating currents supplied to the field winding and the control winding respectively. Suitable speed-reducing gears between the rotor and shaft I5 may be contained within the servomotor housing. The two windings of the motor are supplied with alternating currents of the same frequency which are substantially in phase quadrature. Shaft I5 is rotated in one direction when the control winding current leads the field winding current, and is rotated in the opposite direction when the control winding current lags the field winding current. Thus, a phase reversal of the control winding current reverses the servomotor. When no current is supplied to the control winding, the servomotor stops.

Alternating current which is substantially in phase quadrature with the fundamental-frequency component of excitation current is supplied to the field winding of the servomotor through alternating current connections 18 and a series capacitor l9. Alternating current which is either in phase, or out of phase, selectively, with the fundamental-frequency component of the excitation current is supplied to the control winding of the motor through alternatingcurrent connections 20. Connections 20 are connected across a parallel-resonant circuit which consist of an inductor 2| and a capacitor 21 connected in parallel and resonant to fundamental-frequency electric signals. This resonant circuit is connected, in series with a direct-current blocking capacitor 23,across the signal winding, as shown.

Assume that a control current is applied through connections II which produces a net control flux in saturable legs 2 and 3, and thus causes unequal degrees of magnetic saturation to occur in the two saturable legs. An electric signal appears across the signal winding, which causes alternating current to flow through the control winding of the servomotor. The servomotor then rotates shaft l5, and thereby adjusts the angular" position of magnet I3 to change the magnitudeor' direction, or both, of that portion of the control flux produced by the permanent magnet. This adjustment continues until a null position is reached,'at which that portion of the control flux produced by magnet I3 is equal and opposite to that portion of the control flux produced by the control current. The signal-voltage thenbecomes zero, and theservomotor stops. The angularposition of magnet I3, when so adjusted,

corresponds to the magnitudeand direction of;

the control current.

To obtain easily read indications of the-magnitude and direction of control current, I may attach to shaft II apointer 24 and provide a scale zi suitably calibrated in appropriate units. Al-' ternatively, or in addition, I may connect shaft l5 to a recorder, or to any other mechanism which I may desire to actuate in accordance'with control current values.

It will be understood that my invention is not limited to the specific embodiment herein illus,

trated and described, and that the followingleast a portion of a magnetic flux termed thecontrol fiux, a signal winding, a magnetic core member having at least two saturable parts through which the controljfl'ux may pass,isaid' permanent magnet being adj ustable in position relative to said core member for varying the magnitude and direction of its portion of the control flux, an excitation winding, and alternating current connections and a half-wave rectifier in series with said excitation winding for applying pulsating direct current thereto, said excitation winding being arranged to provide pulsating magnetic flux which in its relation to the control flux is simultaneously additive in one of said saturable parts and subtractive in the other, said signal winding being arranged in balanced relation to equal amounts of pulsating flux in said two saturable parts, whereby an induced alternating voltage signal occurs across said signal winding only as said parts are unequally saturated by action of the control flux.

2. A saturable magnetic core control device responsive to an electric current of variable magnitude and direction termed the control current, comprising a signal winding and connections for applying the control current thereto, thereby producing a potrion of a magnetic flux termed the control flux, a permanent magnet producing another portion of the control flux, a magnetic core member having at least two' saturable parts through which the control flux may pass, said permanent magnet being adjustable in position relative to said core member for varying the magnitude and direction of its portion of the control flux, an excitation winding, and alternating current connections and a half-wave rectifier in series with said excitation winding for applying pulsating direct current thereto, said excitation winding being arranged, to provide pulsating magnetic flux which in its relation to the control flux is simultaneously additive in one of said. saturable parts and subtractive in the other, said signal winding being arranged in balanced relation to equal amounts of pulsating flux in said two saturable parts, whereby an induced alternating voltage signal occurs across said signal winding only as said parts are unequally saturated by action of the control flux.

3. A saturable magnetic core control device responsive to a magnetic flux of variable magnitude and direction termed the control flux, comprising a magnetic core member having at least two saturable parts through which the control flux may pass, an excitation winding, alternating current connections and a half-wave rectifier in series with said excitation winding for applying pulsating direct current thereto, said excitation winding being arranged to provide pulsating magnetic flux which in its relation to the control flux is simultaneously additive in one of said saturable parts and subtractive in the other, a signal winding arranged in balanced relation to equal amounts of pulsating flux in said two saturable parts, whereby an induced alternating voltage signal occurs across said signal winding only as said parts are unequally saturated by action of the control flux, a servomotor having a field winding and a control winding, said servomotor being of av type which rotates in either direction selectively depending upon the phase relation between alternating currents supplied to said field winding and said control winding respectively, electrical connecting means to supply said field winding with alternating current which is substantially in phase quadrature with the fundamental-frequency alternating component of the pulsating current applied to said excitation winding, and electrical connecting means for transmitting fundamental-frequency signals from said signal winding to said control winding,

6 whereby operation of said servomotor is controlled by the control flux.

4. A saturable magnetic core control device responsive to an electric current of variable magnitude and direction termed the control current, comprising a signal winding and connections for applying the control current thereto, thereby producing a portion of a magnetic flux termed the control flux, a permanent magnet producing another portion of the control flux, a magnetic core member having at least two saturable parts through which the control flux may pass, said permanent magnet being adjustable in position relative to said core member for varying the magnitude and direction of its portion of the control flux, an excitatio winding, alternating current connections and a half-wave rectifier in series with said excitation winding for applying pulsating direct current thereto, said excitation winding being arranged to provide pulsating magnetic flux which in its relatio to the control flux is simultaneously additive in one of said saturable parts and subtractive in the other, a signal winding arranged in balanced relation to equal amounts of pulsating flux in said two saturable parts, whereby an induced alternating voltage signal occurs across said signal winding only as said parts are unequally saturated by action of the control flux, a servomotor having a field winding and a control winding, said servomotor being of a type which rotates in either direction selectively depending upon the phase relation between alternating currents supplied to said field winding and said control winding respectively, electrical connecting means to supply said field winding with alternating current which is substantially in phase quadrature with the fundamental frequency of the alternating components of the pulsating current applied to said excitation winding, electrical connecting means for transmitting fundamental frequency signals from said signal winding to said control winding, whereby operation of said servomotor is controlled by the control flux, and mechanical connections between said servomotor and said permanent magnet such that operation of said servomotor adjusts the position of said magnet to balance the two portions of control flux, whereby said magnet is adjusted automatically to positions which respectively correspond to unique values in magnitude and direction of the control current.

5. A saturable magnetic core control device responsive to an electric current of variable magnitude and direction termed the control current, comprising a signal winding and connections including a series reactor for applying the control current thereto, thereby producing a portion of a magnetic flux termed the control flux, a permanent magnet producing another portion of the control flux, a magnetic core member having at least two saturable parts through which the control flux may pass, said permanent magnet being adjustable in position relative to said core member of varying the magnitude and direction of its portion of the control flux, an excitation winding, alternating current connections and a half-wave rectifier in series with said excitation winding for applying pulsating direct current thereto, said excitation winding being arranged to provide pulsating magnetic flux which in its relation to the control flux is simultaneously additive in one of said saturable parts and subtractive in the other, said signal winding being arranged in balanced relation to equal amounts of pulsating flux in said two saturable parts, where-,- by an induced alternating voltage signal occurs across said signalwinding only as said parts are unequally saturatedby action of the control flux, a servomotor having a field winding and a control winding, said servomotor beingof a, type which rotates in either direction; selectively :depending upon the phase relation between alternating currents supplied ,to said field winding and said control winding respectively, electrical connections including a series, capacitor for supplying, said field winding with alternating currentwhich is substantially in phase quadrature with the fundamental-frequency alternating component; of the pulsating current supplied to said excitation winding, a parallel resonant circuit connected in series with a direct-current blocking capacitor across said signal winding, said resonant circuit consisting; of areactor and a capacitor in parallelnwhich are resonant to; fundamental-frequency signals, electrical means connecting said control, winding across said, resonant circuit,

whereby operation of said servomotor :is controlled by the control flux, and mechanical connections between said servomotor and said permanent magnet such that operation of said servomotoradjusts the position of said magnet to balance the two portions of control flux, whereby saidmagnet is. adjusted automatically to positions which respectively correspond to unique values in magnitude and direction of the control.

applying the control current thereto,-ther eby i foviding a portion of a magnetic flux termedthe control flux, altransverselymagnetized perma nent magnet positioned within the gap of said center leg to provide another portion of the con-,

trol flux, said permanent magnet being rotatable relative to said core member of varying the magnitude and direction of its portion of the control flux, said signal winding consisting of two seriesconnected balancedhalves so wound upon said two legs respectively that the control flux passes inthe same direction through the two saturable legs, whereby an inducedalternating voltage sig:

nal occursacross the whole of said signal winding only as saidlegs are unequally saturated by. ac-

tion of the control flux, a-seryomotor having'va,

field winding and a control winding-,;said servomotor being of a type which rotates inaeither direction selectively depending, upon the phase relation between alternating current appliedto. said field winding and said control winding respectively, electrical connecting means to supply said field winding with alternating current which.

is substantially in phase quadrature with the fundamental-frequency alternating component of the pulsating current applied to said excitation winding. electrical connecting means for transmitting fundamental-frequency signals from said.

signal winding to said controlwinding, .whereby operation of said servomotor is controlled by the control flux, and mechanical connections between said servomotor and said permanent magnet such that operation of said servomotoradjusts the position of said magnet to balance thettwo portions of control flux, whereby said magnet is adjusted automatically topositions which'respec-- tively correspond to unique valuesin magnitude and direction of the control current.

ReferencesCited in the file of this patent UNITED STATES PATENTS.

Number Name Date 2,259,647 Logan Oct. 21, 1941 2,552,952 Gachet May15, 1951- 

